Boomerang



Sept. 16, 1969 J, s'ro 3,467,385

BOOMERANG Filed Oct. 18, 1965 INVENTOR United States Patent 3,467,385 BOOMERANG James F, Liston, 866 Hare Ave., Ottawa 13, Ontario, Canada Filed Oct. 18, 1965, Ser. No. 497,019 Int. Cl. A63b 65/00 US. Cl. 273-106 2 Claims ABSTRACT OF THE DISCLOSURE An aerodynamically formed toy comprising at least two aerodynamically shaped lifting surfaces formed of soft and resilient material having a relatively heavy tip, which lifting surfaces known as blades are connected together through a light weight and durable central hub by means of a malleable adjustable connection which allows the lifting surfaces to be rotated about their longitudinal axes thus providing angular deformation of the lifting surfaces to produce various angles of incidence while sustaining the deformed adjusted position, so that the toy may be adjusted to follow a variety of flight paths.

Background of the invention Boomerangs are fascinating playthings, but their satisfactory operation depends upon critical relationships between their two blades, probably the most important relationships being between the pitch of the two blades, and between the related lift and drag of the blades and the weight of the boomerang. When constructing boomerangs of rigid material, such as the traditional ash wood, it is discouragingly easy to create 'an inoperable boomerang, which cannot be made operable merely by removing more material, and so it is scrap.

Summary of the invention Boomerang flight is a combination of gliding with flywheel or gyroscopic action. In order to keep the boomerang airborne for a satisfactory length of time, the lift of the blades must be adequate to support the weight of the boomerang at the speed of rotation existing throughout the flight. The spin imparted in throwing diminishes steadily due to the drag of the air on the blades, but at a rate influenced by the polar moment of inertia of the boomerang. A rigid boomerang must be designed and fabricated very accurately to be operable, since the only adjustment possible is to increase the polar moment of inertia by adding weights, as is Well known in the art. However, this adds to the weight that must be carried through the flight.

It is an object of this invention to make boomerangs with adjustable pitch blades. Since the tilt of the blades for an operable boomerang is within the range of 0 to degrees, both lift and drag will be increased by an increase in tilt within this range. In the simplest models, this is the only adjustment provided.

Traditional boomerangs are primarily weapons, capable of flights of a hundred yards, and also capable of inflicting injuries. While certain variants of the invention are suitable for use in full size boomerangs, it is a further object to make light, flexible boomerangs 3,467,385 Patented Sept. 16, 1969 ice Description of the drawings In the drawings which illustrate various embodiments of the invention:

FIG. 1 is a partly sectioned plan view of a plastic boomerang molded onto a wire frame,

FIG. 2 is a view of section 11-11 of FIG. 1,

FIG. 3 is a plan view of part of a moulded plastic boomerang with a sheet metal insert,

FIG. 4 is a view on section IV-IV of FIG. 3,

FIG. 5 is a view on section VV of FIG. 3,

FIG. 6 is a sectioned plan view of part of a foamed plastic boomerang moulded onto a wire frame,

FIG. 7 shows a blade with a stub fitted to a resilient hub, the hub shown in section,

FIG. 8 is a section elevation of a different form of hub, and FIG. 9 shows a fuselage adapted to use the same blades as the boomerang of FIG. 7 in building a glider toy.

Description of the preferred embodiment In the variant shown in FIGS. 1 and 2, the boomerang 1 comprises a pair of curved blades 2 tapering out from a solid centre section 3 to larger solid tip sections 4. Wire frame 5 is embedded in the solid sections as shown, and covered by a flat skin 6. Each tip section may be provided with a weight well 7 into which tip weights may be inserted through 'a slot 8. Any suitable weights, such as BB shot or washer slugs, may be used to weight the tips. Where polyethylene is used, flat sheet 6 will have to be welded on by heat. When other plastic materials are used, sheet 6 may be stuck on with suitable adhesive or solvent. Low density polyethylene is favored because of its toughness and resiliency. Soft iron wire of about or 4 inch diameter is suitable for the frame.

In FIGS. 3, 4, and 5, boomerang 10 is moulded with heavy tips 11, of airfoil shape, joined by thinner curved sections 12 to a central section 13, which comprises an angled corner with a curved cross-section, the edges of this section being bent inwardly to form lips 14 retaining a sheet metal insert 15 firmly in place, as shown in FIG. 4. Of course, this variant could be finished with a welded on skin like the boomerang of FIGS. 1 and 2, but it is cheaper to merely heat and deform the lips 14 over the edges of the insert. The insert may be of soft sheet iron of the order of .020" thick.

In FIG. 6, an airfoil blade 20 of strong foamed plastic, for example of 2 lb./cu. ft. Styrofoam known in the trade as Pelaspan, is moulded onto soft iron wire frame 21. An accumulation of wire 22 is formed at the tips, either by bending and resistance welding as shown, or by twisting the required amount of wire together, in order to provide enough weight in the tips to maintain a spin. To facilitate locating the frame in the die, crimps may be provided in the wire, which will engage the inner surfaces of the die when it is closed, but will appear in the finished product only as tiny spots in the surface of the plastic skin.

It will be observed that the three variants described above each comprises relatively soft, light plastic blades combined with structural elements of stronger material which may be deformed to change the tilt of the blades, and which are sufficiently rigid when deformed to resist deflection from their adjusted position during throwing and flight of the boomerang. Thus, the toy has the desirable qualities of the soft, resilient plastic, which is harmless and durable in use, rebounding from accidental collisions without damage to either the boomerang or the person or object contacted, and at the same time is capable of being adjusted accurately for perfect flights. This requires accuracy to a fraction of a degree, which could not be achieved merely by copying a conventional boomerang in moulded plastic.

The variant of FIG. 7 achieves adjustability in a different way, by providing airfoil blades 30 of any suitable material, for example of hollow moulded plastic, with an integral stub 31 having a head 32 of slightly greater diameter and with a contour suitable for facilitating insertion into the holes 33 of a resilient hub 34. For greater security, each hole may be surrounded at its inner end by a flat area 35 at right angles to the hole axis, so that stub heads 32 will bear on the inner surface of the hub around their entire periphery. As shown, the holes may radiate from the centre of the hub with different angles between each pair of holes, thereby allowing, in the example shown, boomerangs to be assembled with angles between the blades of 75 85", 95, or 105 This range includes the best angles for operable boomerangs. The blades are finished by inserting heavy tips 36a, which may be retained by lugs 37 sprung into cooperating holes in blades 30.

The outer contour of hub 34 is as shown for variant 34a in FIG. 8, i.e. a spherical surface ending in flat top and bottom surfaces. In the variant of FIG. 7, the thickness of the hub wall at the holes may be slightly greater than the length of stubs 31 between the blades and the stub head, so that considerable force is needed to pop the stub heads past the inner ends of the holes. Alternatively, the arcuate blade bases 38 may have a smaller radius of curvature than that of hub 34, so that deflection of the blade bases is necessary in order to pop in stub heads 32. In either case, the result must be a joint with sufiicient friction between the engaging surfaces of the blade and hub to resist deflection during the throw, which creates substantial centrifugal force tending to cause the blades to fly out radially, and the air reactions during flight. Popping out of blades on landing or collision is not objectionable, since it saves breakage. For blades of the order of six inches long, stubs at least /2 inch in diameter are recommended, in order to have adequate strength.

The hub variant 34a of FIG. 8 is made in two halves, using somewhat less resilient material, since the holes need not be stretched by pushing in stub heads; a firm type of nylon is suitable, as is polypropylene. The half holes should be slightly undersize for the stubs 31, so as to provide an interference fit when clamped on by tightening nut 40 onto bolt 41. For lightness, these are also made of nylon or other light, strong plastic. While this hub may be made of matching halves, i.e. right and left hand, this requires two die sets. Since only a single pair of holes will be used at a time for a two bladed boomerang, identical half hubs requiring only one die set will be satisfactory, since a mismatch at the unused holes is immaterial.

Blades and hubs as shown in FIGS. 7 and 8 may be supplied for sale as a kit, to which may be added a tubular fuselage 50 as shown in FIG. 9. Holes 51 are spaced apart at distances equal to the space between a blade stub 31 and either blade base corner 39, so that when a blade stud is inserted in any intermediate hole of a row, as shown in FIG. 9, the corners may be engaged with the next adjacent holes. A limited tilt adjustment may be made, but variations in flight pattern are achieved primarily by varying the longitudinal position of the blades along the fuselage. A rudder 52 may be provided, either moulded integrally with the fuselage or in the form of a short blade with a stub. Two other such blades (not shown) may be provided for the rest of the tail assembly, or the kit may simply include four blades of the same size or boomerang blades. When blades 30 are used in the glider, light tips 36b are plugged in, since heavy tips would be a handicap to the glider assembly. Depending upon the method of making fuselage 50, the nose may be moulded integrally or a separate nose cone 53, as shown, may be plugged in.

It will be apparent that the basic idea may be embodied in other ways than those disclosed, for example by reversing the stub and hole arrangement to provide a hub with long, tapering stubs within the self-locking range of tapers, and co-operating bores in the blades. However, the variants shown in the drawings and discussed in the disclosure above are believed to cover the most economical and effective ways of providing a safe, durable, adjustable boomerang for use as an educational toy. A further variant, more economical than durable, may be made by enveloping the wire frame of FIG. 6 with a softer and more resilient foamed plastic such as foamed polyethylene, which is sufliciently flexible to withstand the twisting at the corner necessary in adjustment. Such a variant is cheap enough for use as a premium or as a very cheap toy, and will have as much durability as the public expects from a cheap toy. The Pelaspan used in the disclosed foam plastic variant, of course, is too brittle to stand the twist ing, which is why the centre is left bare. Failure of the foam plastic in use, of course, will not cause any hazard, since the wire frame is light and without sharp edges. In variants using sheet metal inserts, there should be no skirnping in covering the edges with an adequate thickness of plastic, to guard against any possibility of a metal edge becoming exposed during use.

I claim:

1. A boomerang comprising at least two airfoil shaped blades formed of a relatively soft, resilient material, and means connecting said blades together with their longitudinal axes substantially in a common plane, the lift of each said blade during the flight of said boomerang being dependent upon the tilt of said blade about its axis, said means being adjustable to permit said blades to be tilted about their axes and sufliciently rigid to retain said blades in their adjusted positions by resisting the forces occasioned by the throwing and subsequent flight of said boomerang, whereby said boomerang may be adjusted to follow a variety of flight patterns; wherein said connecting means comprises a hub, and cooperating stub and socket means joining each said blade to said hub; said hub comprising an annulus of relatively resilient material, said socket means comprising holes in said annulus, and said cooperating stub means comprising a stub integral with each said blade; said stubs having heads with one cross section of greater area than that of said holes, whereby said hub will be distended by insertion of said stub heads through said holes and said heads will resist withdrawal of said blades from said hub; the thickness of said annulus at said holes being slightly greater than the length of said stubs exclusive of their heads, whereby said stubs will be in tension after insertion.

2. A boomerang as claimed in claim 1, said annulus having a spherical outer surface and said blades having arcuate bases adjacent to said stubs, the radius of curvature of said bases being smaller than the radius of curvature of said surface, whereby said arcuate bases and said hub surface must be forced into conformation in order to fully insert the stub heads into the holes, and so ensuring a tight engagement to maintain the blades in adjusted position relative to the hub during use of the boomerang.

References Cited UNITED STATES PATENTS Bradley 273106 Gillen 46-82 Tompkins 4625 Wing 4674 FOREIGN PATENTS 11,299 12/1909 France.

RICHARD C. PINKHAM, Primary Examiner PAUL E. SHAPIRO, Assistant Examiner US. Cl. X.R. 

